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1 2004 Poultry Science Association, Inc. Hatchability and Early Chick Growth Potential of Broiler Breeder Eggs with Hairline Cracks D. M. Barnett, B. L. Kumpula, R. L. Petryk, N. A. Robinson, R. A. Renema, and F. E. Robinson 1 Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada, T6G 2P5 Primary Audience: Hatching Egg Producers, Hatchery Specialists, Researchers SUMMARY Eggs with hairline cracks are often placed in incubators, as they can appear structurally sound and, hence, capable of producing a saleable chick. The relative incubation weight loss, embryonic mortality, hatchability, and early chick growth rates associated with normally shelled broiler eggs and those with hairline cracks under practical conditions are not known. To determine the incidence of hairline cracks, eggs from 5 commercial flocks of various strains were candled, and equal numbers of hairline-cracked and normal eggs were collected and incubated for 21 d. All eggs were weighed and candled at 18 d, and any nonviable eggs were removed. All unhatched eggs remaining after 21 d of incubation were broken open to assess the stage of embryonic development. Transfer weights, hatchability, and chick hatch weights were lower (P < 0.05) in hairline-cracked as compared with normal eggs, whereas the percentage of weight loss was higher in hairline-cracked eggs. Hatchability was 74.37% for normal eggs as compared with 50.52% for hairline-cracked eggs. The incidence of mid (8 to 14 d of incubation) and late (over and including 15 d of incubation) embryonic mortality was higher in hairline-cracked eggs as compared with normal eggs. Significantly more hairline-cracked eggs were contaminated, broken, or both during incubation as compared with normal eggs. An increase in chick mortality was associated with hairline-cracked eggs compared with the normal eggs during the 14-d chick growth trial. Hairline cracks reduced hatchability of hatching eggs, increased the likelihood of contamination in the incubator due to putrefaction, and resulted in greater chick mortality. For these reasons, hairline-cracked eggs should not be incubated. Key words: shell quality, embryo mortality, chick weight, hatchability, fertility, incubation egg weight loss 2004 J. Appl. Poult. Res. 13:65 70 DESCRIPTION OF PROBLEM Losses from cracked eggs can be a significant problem in the broiler chicken industry. It has been reported that 6.4% of broiler breeder eggs are not collected due to shell damage [1] Shell damage can be classified as either a complete crack or as a hairline crack. A hairline crack occurs when the shell is broken, yet the shell membranes remain intact [2]. A complete crack occurs when both the shell and shell membranes are broken, thus increasing the porosity 1 To whom correspondence should be addressed:

2 66 and permeability of the egg. Completely cracked eggs are not placed in commercial hatcheries due to the risk of severe dehydration and bacterial contamination [3]. Currently, hairline-cracked eggs may be set in commercial hatcheries. However, minimal information is available regarding their water loss, hatchability, or growth rates as compared with normal, intact eggs. The eggshell performs a dual function during embryonic development. The shell has to be strong enough to protect the embryo from external insults, yet it must have adequate porosity to supply the embryo with oxygen by facilitating the movement of respiratory gases across the shell [4, 5]. During development, oxygen, carbon dioxide, and water vapor are transported through the pores of the shell [6]. Proper gas exchange across the shell is crucial to the viability of the embryo. Water loss is essential to prevent a relative increase in water content due to the formation of metabolic water [6]. As water evaporates during incubation, it is replaced by gas molecules that form the air cell, which should occupy about 15% of the egg volume prior to hatching [7]. Increasing shell porosity and permeability will increase the oxygen uptake of the embryo until a maximum rate is reached, after which further increases in shell porosity and permeability have little effect [4]. Therefore, oxygen availability is not a limiting factor for embryos within highly permeable, porous shells, but rather there is the danger of dehydration [8]. During incubation, eggs should ideally lose a quantity of water equal to 12% of their initial mass [3]. Water loss exceeding 20% of initial egg mass causes increased mortality and subsequent dehydration of the embryo, thus decreasing hatching success [3]. When the membranes are broken or exposed to bacteria for longer periods or to higher concentrations of bacteria, a greater risk of microbial contamination is possible, leading to embryonic death. The objective of this study was to determine whether chicks from eggs with hairline cracks hatch and grow normally compared with eggs with intact shells. MATERIALS AND METHODS Management and Experimental Design The University of Alberta s Faculty of Agriculture, Forestry, and Home Economics Animal JAPR: Research Report Policy and Welfare Committee approved this protocol according to the Guide to the Care and Use of Experimental Animals [9]. Hairlinecracked eggs and normal eggs were collected from 5 sources (5 different broiler breeder flocks) provided through a commercial hatchery [10]. The 5 breeder flocks ranged in age from 48 to 56 wk of age. The experiment was a 2 5 factorial design, with 2 egg treatments and 5 egg sources. Eggs were candled to determine presence of hairline cracks. Hairline-cracked eggs were determined by candling while the eggs were stored in a darkened egg storage room. A small flashlight was placed on the upper side of each egg, while the eggs remained in egg flats. Eggs were considered to have a hairline crack if they had a crack that was visible by candling but that was not readily apparent upon gross examination. Eggs that had a crack with a disruption of the shell membrane and eggs with defective shells due to calcification problems were not considered to be hairline cracks. For every egg with a hairline crack that was collected, an equivalent weight, normal, noncracked egg was chosen from the same tray. All eggs were marked for identification and weighed. We collected of 396 hairlinecracked eggs and 396 normal eggs and stored them for 2 d at 15.2 C prior to incubation. The eggs were set for 18 d in a Jamesway incubator [11] at 37.2 C and a humidity of 84 C wet bulb. On d 18 of incubation, the eggs were removed from the incubator, weighed, and candled. All infertile and contaminated eggs were discarded. Eggs that contained live embryos were placed into hatch trays containing singleegg pedigree baskets. Trays were placed into a Jamesway hatcher [11] under the same conditions as described above. Each incubator tray (flat) contained up to 34 eggs. Each tray contained eggs of a common type (hairline or normal) from a single source. This tray of eggs was transferred to a single drawer in the hatcher. Three replicate incubator trays and hatcher drawers per interaction of egg type and egg source were available. On 21 d, the chicks were removed from the hatcher, and all live chicks were feather sexed, weighed, and neck tagged for identification purposes. Any unhatched eggs were broken open to assess hatchability status, and for dead em-

3 BARNETT ET AL.: VIABILITY OF CRACKED EGGS 67 TABLE 1. Set weight, transfer weight, percent weight loss, chick weight, and percentage chick weight of original egg in hairline-cracked and normal eggs All eggs set Egg weight loss Eggs with live embryos only from setting to Relative chick Egg weight at Egg weight at transfer (% of fresh weight (% of set Treatment setting (g) transfer (g) egg weight) Chick weight (g) weight A ) Egg type Normal shell a b a a Hairline crack b a b b SEM Egg source c c ab d b b bc a c b a a c a a bc b bc b a c c b d b SEM a d Means within a main effect and within a column with no common superscript differ (P < 0.05). A Weight calculation of live chicks only. bryos the stage of embryonic mortality was recorded. Any live-in-shell chicks and cull chicks were euthanized by cervical dislocation. Eggs were considered to be contaminated if they showed visible evidence of rotting putrefaction during incubation or at the break out of the hatch residue. Chicks were reared for 14 d, in 40 pullet cages with 10 chicks per cage (3,100 cm 2 ). The chicks were separated into 2 groups of 10 for each interaction of treatment (source shell type) and sex. Each cage contained 2 nipple waterers. The chicks were exposed to a 23L:1D schedule and were housed at a temperature of 29.4 C. Chicks consumed a 23% CP, 3,200 kcal/ kg ME broiler starter ration ad libitum. The incidences of mortality during this period were noted and weighed. All surviving chicks were weighed on d 14. All data were analyzed using SAS software [12] with incubator tray, hatcher tray, or rearing cages as the experimental unit [13]. RESULTS AND DISCUSSION Fertility and Hatchability Characteristics The incidences of hairline cracks for egg sources 1 to 5 were 0.74, 0.50, 0.49, 0.43, and 0.71%, respectively. No difference in egg weight was noted at setting between hairline-cracked and normal eggs. Set weights differed significantly between egg sources ranging from 63.0 to 67.8 g (Table 1). Significant differences were apparent in percentage of weight loss between the hairline-cracked eggs and the normal eggs from setting to transfer (Table 1). Hairlinecracked eggs lost 17.0% of fresh egg weight, compared with normal eggs, which lost only 13.3%. The hairline-cracked eggs lost approximately 5% more weight than what is considered the ideal weight loss. Consequently, chicks that hatched from hairline-cracked eggs with a hatch weight of 43.6 g were significantly smaller than the normal egg hatch weights of 45.0 g (Table 1). Egg transfer weight, percent weight loss, and chick hatch weight differed significantly among egg sources (Table 1). This difference can be attributed to flock variation, including strain, diet, and hen age. As expected, fertility did not vary between normal and hairline-cracked eggs (Table 2), as fertilization takes place prior to shell formation. Fertility varied among the source flocks (77.5 to 100.0%, Table 2) for the reasons mentioned above. The normal eggs exhibited 80.9% hatchability, and the hairline-cracked eggs showed 56.4% hatchability (Table 2). The relatively poor hatchability of the normal eggs is likely an artifact of the advanced age of the flocks rather than problems with the functioning of the incubators and hatchers. Dehydration and microbial contamination are 2 major factors contributing to

4 68 JAPR: Research Report TABLE 2. Percentage fertility, hatchability, and embryonic mortality of normal and hairline-cracked eggs Embryonic mortality B Hatchability Early Mid Late Broken or Fertility A Hatchability A of fertile (1 to 7 d) (8 to 14 d) (15 to 21 d) Cull contaminated Treatment (%) (%) (%) (%) (%) (%) (%) (%) Egg type Normal shell a a b 4.62 b b Hairline crack b b a a a SEM Egg source b ab a 0.78 c 1.50 b ab ab ab 0.61 c 4.94 a b c c a 0.78 b a b b b 0.00 b b a a 0.00 c 0.00 b SEM a c Means within a main effect and within a column with no common superscript differ (P < 0.05). A Percentage of all eggs set. B Percentage of all fertile eggs. reduced hatchability of hairline-cracked eggs. The rate of dehydration grows with the increased permeability and porosity caused by the crack. The subsequent decrease in hatchability noted is consistent with other published results [3]. Normal eggs had a 1.25% incidence of contamination and breakage, as compared with the 5.35% incidence observed in hairline-cracked eggs (Table 2). Increasing the time and concentration of bacterial exposure to the membrane increases the digestion of the membrane by proteolytic enzymes secreted by the bacteria [14]. Once the membrane is penetrated, embryonic death may occur. Hairline cracks increase bacterial exposure to the membrane, thus decreasing hatchability. Narahari et al. [2] concluded that by minimizing excessive moisture loss and microbial contamination, hatchability is significantly improved. Hairline-cracked eggs were more susceptible to breakage due to subsequent handling, possibly suggesting that the shell quality of these eggs is poorer than for normal eggs (Table 2). In this study, the incidence of early dead embryos due to dehydration did not differ between hairline-cracked and normal eggs (Table 2), which was consistent with previously published results [15]. Embryos in early development are thought to be very resistant to a wide rate of desiccation [15]. In the current study, normal eggs had no mid (8 to 14 d) dead embryos, whereas the hairline-cracked eggs had 2.89% mid dead embryos. Embryonic mortality during midincubation is caused by, but not limited to, improper incubation temperature, humidity, ventilation, turning, dehydration, and contamination [16, 17]. Increased permeability and porosity create conditions that dehydrate the egg and cause embryonic mortality [5]. Normal eggs showed a 4.62% incidence of late dead embryos, and hairline-cracked eggs showed 15.53% incidence of late (15 to 21 d) dead embryos (Table 2). Typically, more embryos die during late incubation than in midincubation [15]. Factors that cause embryonic mortality during late incubation are improper incubator and hatcher humidity, temperature, ventilation as well as dehydration, contamination, broken shells, and embryonic malposition [16, 17]. Because shell porosity and permeability influence the water status of the embryo a few days prior to hatching, increased permeability of eggs increases late mortality [8, 18] due in part to contamination. The hatchability of fertile eggs varied significantly among egg sources and ranged from 50.7 to 79.8% (Table 2), whereas the incidence of abnormal and culled chicks did not. Growth Characteristics Shell condition had no influence on 14-d chick body weight (Table 3). These results are similar to those found by Davis and Ackerman

5 BARNETT ET AL.: VIABILITY OF CRACKED EGGS 69 TABLE 3. Growth performance, culling incidence, and mortality during 0- to -14-d growth trial for hairline-cracked and control eggs from egg sources D14 Body Incidence of Incidence of weight at 14 d mortality cull chicks Treatment (g) (%) (%) Egg type Normal shell b 1.00 Hairline crack a 0.00 SEM Egg source b b b b a 0.00 SEM Sex Male Female SEM a b Means within a main effect and within a column with no common superscript differ (P < 0.05). [3], in that water-stressed chicks did not have a reduced growth rate when compared with normal chicks. If the hairline cracks were minor enough to allow the chick to hatch, growth rate was not affected. However, chicks that hatched from normal eggs had a lower incidence of mortality (2.00%) compared with hairline-cracked eggs (7.39%) (Table 3). Although this finding may be due to stress from early dehydration in a portion of the chicks from hairline-cracked eggs, it may also be the result of an introduction of infectious organisms during incubation through contamination. The rate of culling during the 14-d growth period was not affected by egg type. No significant difference among sources in growth rate or the incidence of culling was noted. (Table 3). No significant difference was found between males and females during the 14- d rearing phase for incidence of mortality or culling or for final 14-d weights (Table 3). Chick mortality during rearing varied significantly among egg sources from 1.25 to 12.50% (Table 3). This variation in chick quality during rearing could be due to initial egg size, which varied significantly among egg sources (Table 1), genetic strain, general shell quality, or the nutritional and management regimens of the source flocks. CONCLUSIONS AND APPLICATIONS 1. Hairline-cracked eggs exhibited increased incubation weight loss and reduced embryo viability and hatchability compared with normal shelled eggs. 2. A higher incidence of broken and contaminated eggs was found during incubation in hairlinecracked eggs than in normal eggs. 3. Chicks hatched from hairline-cracked eggs were significantly smaller than chicks hatched from normal eggs, although no significant difference was found in 14-d growth potential. 4. Chicks that hatched from hairline-cracked eggs showed a higher incidence of mortality during a 14-d growth period. 5. Effort should be made to reduce the likelihood of eggs acquiring hairline cracks in egg handling. Candling eggs to detect such cracks may be counterproductive due to the increased egg handling associated with candling.

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